Utility knives generally include a handle and at least one replaceable blade. Because such blades are known to become worn or damaged, utility knife handles generally include provisions to allow a blade to be removed from the handle, so that the blade may be reversed in the handle (in order to provide a new cutting edge for the knife) and/or replaced by another blade. In addition, utility knife handles generally include a blade carrier for supporting the blade and an actuator operably connected to the blade carrier to move the blade and blade carrier between retracted and extended positions.
In the case of many utility knives, the removal of a worn or damaged blade requires that the handle first be opened to gain access to the internal cavity inside the handle, in order to retrieve a spare blade that may be stored inside the handle. Unfortunately, upon opening the handle, the spare blades can fall out and become separated from the handle.
Some utility knife handles include a spare blade holder that releasably retains spare blades by engaging opposite surfaces of each blade with a pair of opposing clip members, and that orients the spare blade transversely relative to the cutting blade in the blade carrier. This arrangement tends to increase the width of the handle because of the spare blade orientation. In addition, it can be difficult to remove a spare blade from the opposing clip members because of the force required to remove it from the grasp of the opposing clip members, and because there is very little of the spare blade exposed rendering it cumbersome to grasp. Further, the number of spare blades that may be stored in such a holder is limited because each additional spare blade increases the thickness of the stacked spare blades, forces the opposing clip members further apart, and correspondingly increases the force applied to the blades by the opposing clip members. The increased force applied by the opposing clip members makes it difficult to add or remove a spare blade from the holder.
In most utility knives, the blade mounted for use is either immovably fixed, or is retractable into or extendable out of the handle. When the blade is constantly exposed, consequent risks of injury to people or objects nearby are possible while the knife is not in use. However, such risk of injury is prevented when the retractable blade is manually retracted into the handle.
To avoid the danger of an exposed blade when the utility knife is not in use, some prior art utility knives include arrangements in which the blade is self-retractable into the handle. Such self-retracting utility knife blades are continually biased towards the retracted position and into the handle using a retractable blade holder. In some such utility knives a toggle linkage is mounted between a fixed point in the handle and the blade holder. A spring normally biases the blade holder rearward, but the spring bias is overcome when one manually biases an operating actuator protruding from the handle, thereby extending the toggle linkage to in turn move the blade to an extended position. However, such prior art utility knives do not permit one to limit the extension of the blade as in an indexed blade carrier design, other than by only partially depressing the operating actuator, which can be awkward. For example, if one desired to extend the blade just enough to function as a box cutter, the user would have to maintain the blade in a position intermediate the fully retracted and extended positions, while working against a bias urging the blade into the retracted position. As a result, it can be difficult to maintain a constant extension of the blade. For example, it can be difficult to maintain a constant extension of the blade having the blade extend just enough to penetrate the box to cut therethrough, while also avoiding extension of the blade to an extent that might cause the blade tip to cut through material contained in the box.
Accordingly, it is an object of the present invention to overcome one or more of the above-described drawbacks or disadvantages of the prior art.